Glass fiber is an inorganic fiber material that is useful to reinforce organic polymer materials that in turn are used to prepare high-performance composites or to reinforce inorganic materials, such as cement, for road construction. The production of glass fiber, a special glass, has been difficult. Therefore, the usage amount of glass fiber is restrained due to its relatively high production cost. The introduction of the tank furnace in 2000 has caused a breakthrough in the art of mass production of glass fiber, by significantly reducing the cost of mass production of glass fiber, thus expanding the fields of application for and usage amounts of glass fiber since then. However, limitations due to the heating method and refractory material associated with tank furnaces, production of glass fiber by tank furnace methods of production require that the high temperature viscosity of the glass composition is limited, that is, it should not be too high. Generally, the forming temperature of a glass composition should be less than 1300° C., and at least 50° C. higher than its liquidus temperature.
The standard glass composition for preparing continuous glass fiber, commonly known as “E” glass, includes the following components in percentage by weight as per the ASTM D578-00 Standard: 0-10% of B2O3, 16-25% of CaO, 12-16% of Al2O3, 52-62% of SiO2, 0-5% of MgO, 0-2% of alkali oxide, 0-1.5% of TiO2, 0.05-0.8% of Fe203 and 0-1% of F2. Melting, clarification and fiber drawing can be done to E glass at low temperature. The forming temperature is generally lower than 1280° C., which meets the requirements of mass production by tank furnace. Production of E glass began approximately in 1940. However, E glass remains the composition of over 90% of glass fiber produced around the world.
In the 21st century, as science and technology develops, improvement of the performance of fiber-reinforced composites is required, thereby requiring glass fiber having better performance characteristics than prior glass fiber. Ordinary E glass fiber, which contains about 7% of B2O3 in percentage by weight, has been unable to meet the performance demands in certain fields of use, including, for example manufacturing of wind turbine blades, high-performance GRP (Glass Reinforced Pipe(s)) and automobile components due to its relatively poor mechanical properties, particularly its monofilament strength.
Boron-free E glass fiber is known, as described for example in U.S. Pat. No. 5,789,329 (“the '329 patent publication”), and improved E glass fiber is known, as described in U.S. Pat. No. 6,136,735 (“the '735 patent publication”). While the boron-free E glass fiber and improved E glass fiber described in those two patents have relatively better mechanical performance than ordinary E glass fiber, neither meet the demands required in such special fields of use as wind turbine blades and high pressure pipes.
Compositions of high-performance glass fiber are known and described, for example, in U.S. Pat. No. 3,402,055 (“the '055 patent” or “the '055 patent publication”), France Patent FR-A-1,435,073 (“the French '073 patent publication”) and Chinese Patent Application CN94111349.3 (“the Chinese '349 publication”). The main component of the high-performance glass fiber described in each of these three patent publications is SiO2—Al2O3—MgO or SiO2—Al2O3—CaO—MgO, each of which is different from SiO2—Al2O3—CaO—B2O3, the main components or ingredients of E glass fiber. Although the glass fibers described in these three patent publications have relatively great mechanical strength and high modulus, the requirements of mass production by tank furnace can not be fulfilled presently.
To be specific, the molding or forming temperature of typical S-2 glass fiber, as described in the '055 patent, exceeds 1500° C., and the molding or forming temperature of R glass fiber, as described in the French '073 patent publication is about 1410° C. The temperatures for melting, clarification and wire drawing operations of these two glass fibers are extremely high and exceed the maximum temperatures that can be reached during tank furnace production. The Chinese '349 patent publication describes a high-performance #2 glass fiber whose forming or molding temperature is about 1245° C., but it liquidus temperature reaches 1320° C. Thus, for the Chinese '349 patent publication glass fiber, the ΔT (the difference between the forming temperature and the liquidus temperature) is −75° C. However, in general a positive ΔT value exceeding 50° C. is required during tank furnace production. Therefore, the glass fibers described in these three patent publications are not suitable for mass production by tank furnace production processes.
Due to the restrictions related to production mode or to failure to achieve mass production of high-performance glass fiber by tank furnace methods of manufacturing, the manufacturing costs and ultimate prices of high-performance glass fibers are extremely high, thereby seriously affecting the total output relative to demand. As a consequence, high-performance glass fiber is typically used only in such fields as aviation, aerospace, national defense, military and the like. There is a high demand for high performance glass fiber in relatively new industries and applications, such as blades for high-power wind turbines, high pressure pipe lines and pressure vessels, for which current production levels of high-performance glass fiber can not meet the demand.